1400-50;late Middle Englishassessen < Medieval Latinassessāre to assess a tax, derivative of Latinassēssus seated beside (a judge) (past participle of assidēre), equivalent to as-as- + sed- (stem of sedēre to sit) + -tus past participle suffix
early 15c., "to fix the amount (of a tax, fine, etc.)," from Anglo-Fr. assesser, from M.L. assessare "fix a tax upon," originally frequentative of L. assessus, pp. of assidere "to sit beside" (and thus to assist in the office of a judge), from ad- "to" + sedere "to sit." One of the judge's assistant's jobs was to fix the amount of a fine or tax. Meaning "to estimate the value of property for the purpose of taxing it" is from 1809; transf. sense of "to judge the value of a person, idea, etc." is from 1934.